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Surface Chemistry — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistrySurface Chemistry5 Marks
Question
What are the main differences between physical adsorption and chemical adsorption ?
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Answer

Differences between Physical Adsorption and Chemical Adsorption.
Physical AdsorptionChemical Adsorption
1.It involves weak physical forces of attraction between adsorbate and adsorbent, i.e., van der Waals forces. It is an exothermic process.It involves transfer of electrons between adsorbate and adsorbent, i.e., the forces operating are similar to those of a chemical bond. It is also exothermic.
2.Physisorption forms multi-molecular layers.Chemisorption forms unimolecular layer.
3.More easily liquifiable gases are adsorbed readilyThe gases which form compounds with the adsorbent are only chemisorbed.
4.Heat of adsorption is low (about 20-40 kJ mol¹).Heat of adsorption is high (about 40-400 kJ mol¹).
5.It is not specific in nature as all types of gas are adsorbed on all solids by weak van der waals forces. It depends on polar nature of adsorbates roughness of surface of adsorbent.It is highly specific in nature and occurs only when there is some possibility of compound formation between the adsorbate and adsorbent.

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